The third Generation Partnership Project (3GPP) has deployed long-term evolution (LTE) to provide increasing future mobile communication services. The wireless cellular communication gradually becomes a part in the people's life and work. In the first version of the 3GPP LTE, i.e., Release 8, Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple-Input Multiple-Output (MIMO) techniques are introduced. The 3GPP Release 10 has been evaluated and assessed by the International Telecommunication Union (IUT), and becomes the fourth generation mobile communication standard, LTE-Advanced. In the LTE-Advanced, Carrier-Aggregation (CA) and relay techniques are introduced, and the uplink/downlink MIMO technique has been enhanced. The deployment of heterogeneous network (HetNet) is also supported therein.
In order to satisfy the market requirement for future communication of home units and the deployment of the large-scale Internet-of-Things (IOT), the 3GPP decides to introduce Machine Type Communication (MTC) in LTE and LTE-Advanced, move the MTC services that are supported by GSM network currently to be supported by LTE network, and define various new types of LTE User Equipment (UE), among which there is a Low-Cost MTC UE which supports MTC services in all duplex modes of the current LTE network and has the following features: 1) a single receiving antenna, 2) the maximum Transport Block Size in the uplink and downlink is 1000 bits; 3) the bandwidth of the baseband of the downlink data channel is lowed to 1.4 MHz, the bandwidth of the downlink control channel is the same with the system bandwidth at the network side, and the bandwidth of the uplink channel and the radio frequency portion of the downlink are the same with those of the MTC UE in the current LTE network. There is also a LOW-Complexity MTC UE and others.
MTC is a data communication service that no human operation is involved. A large-scale deployment of MTC UEs may be used in the security, track, billing, measurement and consumer electronics and others, and more particular, in video monitoring, supply chain tracking, intelligent electricity meter, remote monitoring and so on. A MTC UE requires low power consumption, supports a low data transmission rate and low mobility. The current LTE system is designed for Human-to-Human (H2H) communication services. Therefore, the LTE network supporting MTC UEs to operate in a low-cost and low complexity mode is important to achieve the advantage of the large scale of MTC services and its applications.
Some MTC UEs need to be equipped in the basement of the residential building or locations protected by insulation foils, metal protection window or the thick walls of the traditional building. Compared with the normal UEs (such as phones, notebooks, etc.), the air interface of the devices will suffer more severe penetration loss. The 3GPP has researched on the design and performance assessment of a solution that MTC UEs are provided with additional 20 dB coverage enhancement services. What shall be noted is that MTC UES that are located at a bad coverage area have the following features: a very low data transmission rate, very loose delay requirement, and limited mobility. For such features of MTC UEs, the LTE network may further optimize some signaling and/or channels to support the MTC UEs. The 3GPP demands to provide some LTE network coverage enhancement for the new MTC UEs and other UEs that operate MTC services (for example, with very loose delay requirement), where 15 dB network coverage enhancement for LTE Frequency Division Duplex (FDD) network UEs. Besides, all the UEs that operate MTC services do not need the same coverage enhancement.
For the downlink of the new MTC UEs, the data channel is 1.4 MHz (i.e., 6 Resource Blocks (RBs)) at the baseband, and the control channel can access the whole downlink system bandwidth while the radio frequency portion remains unchanged, i.e., can access the whole system bandwidth. For the uplink, the baseband and the radio frequency portion both remain unchanged. Furthermore, the MTC UEs have a single receiving antenna, and the maximum uplink transmission block size and the maximum downlink transmission block size both are 1000 bits.
For 3GPP LTE UEs that operate MTC services and are in the enhancement coverage, the coverage enhancement design and configuration of the physical channels, such as PDCCH/PDSCH/PUCCH/PUSCH, are to be standardized. According to the discussion of the 3GPP RAN1 #74, for any physical channel that needs re-transmission after the initial attachment, its configuration depends on the eNode B. It is provisioned in the 3GPP RAN2 #85 that the network side can initiate paging on MTC UEs that are in coverage enhancement mode. It is obvious that the paging need to be retransmitted on the physical channel. In the current LTE standard, the paging is transmitted at two stages: the S1AP interface information transmission between Mobility Management Entity and the Base Station and the physical layer information air interface transmission between the base station and the user equipment. In the S1AP interface information, the Mobility Management Entity initiates a paging process on each base station by using paging, and each paging carrying information on the UE to be paged. The base station receives the paging, interprets content contained therein and retrieves Tracking Area Identity list of the UE, and conducts paging on cells that belong to the tracking areas in the list over air interface. Since the base station is unaware of whether the MTC UEs that are paged are in the coverage enhancement mode, the base station needs to page all messages over air interface so that MTC UEs that are in coverage enhancement mode can receive the paging appropriately. This will lead vast waste of spectrum resource. Therefore, in the Release 12 (Rel-12) and the following releases, the paging mechanism for MTE UEs that are in coverage enhancement mode needs to be re-standardized.